The medical benefits of plant salicylates have been enjoyed by people for centuries. Salicylic acid was first isolated in 1839 from the flower buds of an herb, Filipendula ulmaria, which is also sometimes referred to as Spiraea ulmaria. The benefits of plant-derived salicylates prompted intensive research, which led to the commercial production of synthetic acetylsalicylic acid (aspirin) in 1899. Today, aspirin (acetylsalicylic acid) is probably the most widely used drug in the world because of its antipyretic, anti-inflammatory, and analgesic properties.
The development of the acetylated form of salicylate was prompted by the need for a form of the drug that would not cause the gastrointestinal distress associated with the use of salicylic acid. Indeed, acetylsalicylic acid has been shown to have fewer side effects than salicylic acid. Nonetheless, acetylsalicylic acid can promote similar problems.
Most of the pharmacological activity of acetylsalicylic acid is due to the production of salicylic acid. Some noteworthy activities of salicylic acid include general anti-inflammatory properties, increased fibrinolysis, inhibition of glycosaminoglycan synthesis, inhibition of the lipoxygenase pathway, reduction of T-cell adhesion, free radical scavenging, inhibition of prostaglandin biosynthesis, and some anti-carcinogenesis activities.
As mentioned, acetylsalicylic acid was synthesized as a derivative of salicylic acid that exhibited fewer side effects when administered as a therapeutic. Efforts have been made to derivatize salicylic acid and aspirin in various ways to further mitigate gastric irritation. The general strategy for reducing gastric upset has been to chemically derivatize the salicylate molecule to delay the release of free salicylic acid until after it has passed from the stomach.
Wintergreen, or Gaultheria procumbens, contains a very high concentration of salicylate derivatives, reaching concentrations exceeding 10 mg per gram fresh weight of tissue. This concentration is over 20-fold greater than the total salicylate concentration (salicylate and any derivates combined) found in Filipendula, the plant from which salicylic acid was first isolated. Reports disclosing the presence of gaultherin (a salicylate derivative described below) in Filipendula tissues, but not gaultherin recovery yields, are found, e.g., in the abstracts of Barnaulov et al., Rastit. Resur., 13(4):661–669 (1977) and Yeo etal., Saengyak Hakhoechi, 23(3):121–125 (1992).
Methyl salicylate, also known as oil of wintergreen, is responsible for the smell and taste of wintergreen. Although methyl salicylate can be toxic when ingested at concentrations used for topical application, this ester has been shown to have decreased ulcerogenic activity when compared with an equal dose of salicylic acid, as measured by the respective salicylate contents.
Gaultherin consists of methyl salicylate conjugated to the disaccharide, primeverose. When plant tissues are disrupted, the endogenous gaultherin is rapidly lost, presumably by enzymatic hydrolysis with the release of methyl salicylate. This process presumably occurs as a protective mechanism for the plant.
In 1844, Proctor defined gaultherin as a conjugate of methyl salicylate with glucose but claimed that it did not exist within the plant for which it was named. Interest in such conjugates did not recur until nearly 60 years later, when a series of articles was published in France. The authors of these articles [Bridel and Gillon, Comptes Rendus, pp, 609–611 (1928); Bridel and Guignard, Comptes Rendus, pp. 857–860 (1925); Bridel and Guignard, Comptes Rendus, pp. 1421–1423 (1925); Bridel and Guignard, Comptes Rendus, pp. 642–644 (1923); Bridel and Guignard, Comptes Rendus, pp. 991–993 (1923); Goris et al., Comptes Rendus, pp. 871–873 (1919)] described the sugars of these conjugates and defined monotropidoside as a conjugate of methyl salicylate with primeverose, which is a disaccharide of xylose and glucose. These studies were performed with various species, and led to the occurrence of excessive terminology.
Gaultheria procumbens was not examined until 1928, when it was determined that monotropidoside was gaultherin and that gaultherin could only be extracted from Gaultheria with boiling water and calcium carbonate, followed by a series of solvent extractions, including 95% alcohol distillation, extraction with boiling hydrated acetic ether and addition of 95% alcohol [Bridel and Gillon, Comptes Rendus, pp 609–611 (1928)], which gave a final yield of 4 g/kg fresh weight plant material. These combined observations defined gaultherin as a conjugate of methyl salicylate with a disaccharide of xylose and glucose. These references also described an enzymatic activity leading to the hydrolysis of this conjugate; the activity has been attributed to gaultherase, an enzyme known only by its activity. Those terms have been perpetuated by the literature but no current investigations have been performed on either the conjugate or the enzyme. The previous work was summarized in 1931 [Robertson et al., J Am. Chem. Soc., 1881–1888 (1931)], along with a description of the synthesis of gaultherin. Any current literature which includes the terms gaultherin or gaultherase appears to use these terms as defined in the original sources.
An effective method for obtaining useful quantities of gaultherin from natural plant sources is not currently available. The difficulty in obtaining gaultherin from plant tissue resides in the labile or unstable-nature of gaultherin extracts. Upon disruption of the plant tissue, the molecule is immediately hydrolyzed to its individual components, methyl salicylate and the disaccharide primeverose. As noted above, the hydrolysis is believed to be catalyzed by an enzyme referred to as gaultherase [see Robertson et al., J. Am. Chem. Soc., pp. 1881–1889 (1931), and references cited therein]. Regardless of the means by which the hydrolysis occurs, it appears to be immediate and essentially complete, inasmuch as it has led some investigators to conclude that certain plants, most notably Gaultheria procumbens, do not contain gaultherin [see Proctor, Am. J. Pharmacol., Vol IX, No. IV., pp. 22 and 242–250 (1844)].
Compounding the problem is the relatively hydrophilic nature of both gaultherin and the gaultherase activity. Attempts to maximize yield by using an aqueous solvent would lead to high losses due to gaultherase activity; using a non-aqueous or non-polar solvent would lead to lower than maximal yields because of the relatively lower solubility of gaultherin in such solvents, although the gaultherin might be expected to be relatively stable due to a correspondingly lower yield of the destructive gaultherase activity.
U.S. Pat. No. 5,176,913, issued Jan. 5, 1993, to Honerlagen et al. describes a method for preparing a partial extract containing the volatile-in-steam components and further lipophilic components of various plants. Among many plant species, Gaultheria procumbens L. is disclosed as a plant from which an extract can be obtained. Honerlagen teaches a method in which a drying agent is brought into contact with a crude extract to reduce or eliminate the water content of the extract. As disclosed by Honerlagen, the extraction invariably involves the removal of water, whether by use of chemical drying agents or by use of mechanical drying agents such as membrane technology.
Honerlagen isolates lipophilic plant compounds, including both volatile-in-steam and non-volatile-in-steam compounds. Lipophilic compounds are generally recognized in the art as being hydrophobic compounds which are generally not soluble in water. There is no recognition or appreciation in Honerlagen of a method that allows the separation and recovery of gaultherin from any accompanying gaultherase activity to protect gaultherin from hydrolysis. Further, Honerlagen fails to suggest any use for a gaultherin-containing extract.
Thus, a method for recovering gaultherin from plants by extraction under aqueous conditions suitable for extraction of the water-soluble gaultherin while reducing or eliminating gaultherin degradation or destruction, such as hydrolysis due to a gaultherase activity, would be a significant advance.
Additionally, the provision of a therapeutic agent which may be administered to treat inflammatory responses and cardiovascular conditions, including cardiopulmonary conditions, without causing substantial gastrointestinal discomfort would also represent a significant advance.
Furthermore, the provision of methods wherein serum salicylic acid concentrations are increased, without causing substantial gastrointestinal discomfort, would also be a significant contribution to the art, as would the provision of methods of inhibiting tumor cell growth and cyclooxygenase activity, without causing substantial gastrointestinal discomfort.